Medical treatment of several illnesses requires continuous drug infusion into various body compartments, such as subcutaneous and intra-venous injections. For example, diabetes mellitus patients require the administration of varying amounts of insulin throughout the day to control their blood glucose levels. In recent years, ambulatory portable insulin infusion pumps have emerged as superior alternatives to multiple daily injections of insulin using a syringe. These pumps, which deliver insulin at continuous basal rates, as well as, in bolus volumes, were developed to liberate patients from repeated self-administered injections, and allow them to maintain a near-normal daily routine. Both basal and bolus volumes must be delivered in precise doses, according to individual prescription, since an overdose of insulin could be fatal. Therefore, insulin injection pumps must feature high reliability, preventing delivery of any unintentional insulin excess.
Several ambulatory insulin infusion pumps are currently available on the market. Mostly, these devices have two parts: a durable portion, containing a dispensing means, a controller and electronics, and a disposable portion containing a reservoir for insulin, a needle assembly (cannula and penetrating member), and a fluid delivery tube altogether named “infusion set”. Usually, the patient fills the reservoir, attaches the infusion set to the exit port of the reservoir, and then inserts the reservoir into the pump housing.
After purging air out of the reservoir, the delivery tube and the needle, the patient inserts the needle assembly, at a selected location on the body, and then upon subcutaneous insertion of the needle of the penetrating member, withdraws the penetrating member, while leaving the cannula inserted. To avoid irritation and infection, the subcutaneous cannula must be replaced and discarded after two to three days, together with the empty reservoir.
Examples of a first generation disposable syringe-type reservoir and tubes were disclosed in U.S. Pat. No. 3,631,847 to Hobbs, U.S. Pat. No. 3,771,694 to Kaminski, and later U.S. Pat. No. 4,657,486 to Julius, and U.S. Pat. No. 4,544,369 to Skakoon. The driving mechanism of the dispensing means of these devices is a screw thread plunger, which controls the programmed movement of a syringe piston. These devices represent a significant improvement over multiple daily injections, but all suffer from several drawbacks. The main drawbacks are their large sizes and weight of the devices, which are a result of their spatial configurations and relatively large driving mechanisms of the syringe and piston. The relatively bulky device had to be carried in a patient's pocket or attached to the belt. Consequently, the fluid delivery tube was long, usually longer than 60 cm, in order to allow needle insertion in remote sites of the body. These uncomfortable bulky devices with a long tube were rejected by the majority of diabetic insulin users because they disturb regular activities, such as sport activities and swimming. Furthermore, the effect of the image projected on a teenager's body is unacceptable. In addition, the fluid delivery tube excludes some optional remote insertion sites, like the buttocks and the extremities. To avoid the tubing limitations, a new concept of a second generation was proposed.
This new concept related to a skin adherable device with a housing having a bottom surface adapted for contact with the patient's skin, a reservoir contained within the housing, and an injection needle adapted for communication with the reservoir. This skin adherable device was designed to be disposed every 2-3 days similarly to the currently available pump infusion sets.
This design was disclosed in U.S. Pat. No. 4,498,843 to Schneider, U.S. Pat. No. 5,957,895 to Burton, U.S. Pat. No. 6,589,229 to Connelly, and U.S. Pat. No. 6,740,059 to Flaherty. Additional configurations of conventional skin adherable pumps are disclosed in U.S. Pat. Nos. 6,723,072 and 6,485,461.
In these patents, the pump includes one piece and has to be adhered to the patient's skin for the entire usage duration while the needle that emerges from the bottom surface of the device is being fixed to the device housing.
These second-generation skin adherable devices have several limitations:                They waste insulin—a single-piece device must be disposed after each pump replacement (i.e., every 2-3 days) including unused insulin. Further, in cases of site misplacement (scar tissue, bleeding, cannula kinking, etc.), the entire device including fully filled insulin reservoir must be disposed.        They are expensive—the entire device including relatively expensive parts must be disposed after each pump replacement. Thus, the production cost is high and the final product price far exceeds Medicare allowable payments.        They are bulky and heavy—the automatic insertion mechanism employed in these devices occupies substantial volume, as disclosed in for example, U.S. Pat. No. 6,699,218. Thus, although the insertion process ends, the patient must carry the heavy and bulky insertion mechanism (springs, etc.) for the entire usage duration.        
An attempt to eliminate these drawbacks included a two-piece conventional skin adherable dispensing patch unit having two parts:                A reusable part—a first housing that contains the driving and pumping mechanism, electronics and other relatively expensive components.        A disposable part—a second housing that contains components such as reservoir, tubes and batteries, that can last until reservoir is emptied, i.e., usually a few days.        
This concept provides a cost-effective device and allows diverse usage of the device, e.g., the use of various reservoir sizes, various needle and cannula types and effecting of versatile operational modes. There are various applicable types of pumping mechanisms for the two-piece device configuration.
Conventional delivery mechanisms include linear positive displacement pumping mechanism having a rotary wheel with rollers, a stator and a resilient delivery tube. The tube is located between the rotary wheel and the stator.
While the rotary wheel rotates, the rollers continuously “squeeze” the tube in one direction only, displacing the fluid within the tube from the reservoir towards the exit port provided at the housing. The stator is biased by a spring and is pressed towards the delivery tube against the rotary wheel, preventing coarse movements of the tube.
The conventional delivery mechanism devices suffer from several limitations:                The devices are expensive—each part (disposable and/or reusable) is enclosed within a different housing. Since the disposable part should be often replaced e.g., every 3 days, its housing becomes a major cost factor. Additional cost increase occurs when the stator is configured to be a part of the disposable part.        Sealing hurdles—it is very difficult to manufacture the two parts with a perfect connection due to tolerances and inaccuracies of assembly causing imperfect sealing in parts' connection.        Fluid delivery inaccuracies—delivery tube, rotary wheel and stator are not necessarily located in the same part of the dispensing patch unit (e.g., the stator and the delivery tube are located in the disposable part, while the rotary wheel is located in the reusable part). When connecting the disposable and reusable parts together, the matching of these three components may be mechanically imperfect due to manufacturing tolerances and inaccuracy of assembly. This can cause inaccurate fluid delivery.        The devices are not safe—an initial connection of the reusable part and the disposable part is done by the patient and not in the factory. Therefore a fault connection may happen leading to drug over- or under-dosing.        Status of reservoir content—since the reservoir is located within the disposable housing, the patient is not aware of fluid status in the reservoir during the priming procedure, i.e., while filling the reservoir, the patient is not aware of the current amount of fluid disposed within the reservoir.        
Another drawback of existing skin adherable drug infusion devices is associated with the process of insertion. In cases of fault insertions, the whole device must be discarded including the fluid within (i.e., pre-used insulin). This process is cumbersome and costly,
In view of the foregoing, it would be desirable to provide improved systems, methods, and devices for sustained medical infusion of fluids.